Radio navigation system



26, 1952 c. E. HASTINGS 2,608,685

RADIO NAVIGATION SYSTEM N a: N w u Il g: 3? \M/ g; g g: i N INVENTORI i I Charle-sEJlggz'inw ATTORNEYS C. E. HASTINGS RADIO NAVIGATION SYSTEM Aug. 26, 1952 3 Sheets-Sheet 3 Filed Dec. 29, 1949 INVENTORL Chacles Jiafli gg 'KWQJA/MWO ATTORNEYS determining position with Patented Aug. 26, 1952 Hastings Instrument Company, Inc., Hampton, Va., a corporation of Virginia AppIieation December 29, 1949, Serial No. 135,596"

10 Claims. (01. 343-405) This invention relates to a navigation system and method operable on the principle of phase comparison of the beat frequency between the signals of a .pair oftransmitters asdetected at spacedpoints. I P

It is an object of the present invention to provide a navigation systemand methodcapable of an'extremely high degree ofaccuracy. f

It is a further objelctof this invention'to provide a navigation system'andlmethod"capable of determining position substantially instantaneously, without regard to previous knowledge of position or tracking,

A further object is to provide'a' navigation system and method employingstandard radio communication unitsi Another object i is- 'to provide a system and method for determining theposition of a mobile object'either at the object -or at a fixed station, the latter alternativerequiring a single transmitter and n otherequipment on the moving object. V a

Further objects will be inpart' obvious and in part pointed out hereinafter.

The invention and the novel features thereof may best be made clear from the following description and the accompanying drawings, in which:

Figure l is a blocl; diagram illustrating an exemplary embodiment of the, invention, showing the basic radio communication units employed therein; 7 a v Figure 2 is a diagram corresporiding generally to Figure 1, illustrating one modeof operation of thesysteinand i Figure 3 is a block'diagrain illustrating an alternative embodiment of'the invention, adapted to determine position of a mobile transmitter at the mobile position v j Referring to the'drawin'gs, inFigure 1 is shown .a mobile transmitter ,iwhichmay be carried on a ship, aircraft or other mobile object, adapted to transmit at a fixed frequency. The mobile transmitter II, it will'be understood, represents merely a transmitter of unknown position, and need not necessarilybe moving nor even movable. In conjunction with the mobile transmitter is employed a stationary reference transmitter I2, located at any convenient fixed position within range of the receivers. If the mobile transmitter be operated over water, the reference transmitter may conveniently be located at a suitable point on land, for example near shore line l3. Reference transmitter is a so adapted to transmit at a fixed frequency, and is tuned'to transmit at a different frequency from that of transmitter i I. The frequency difference, preferably, is within the audio range; a differenceof 400cycles for example being entirely satisfactory, whereby the system need utilize but a singleassigned radio frequency channel. A receiver adapted to receive both transmissions'and' detect the beat frequency therebetween willobvious'ly detect the same beat frequency wherever located. However, it will be recognized that the phase of thedetected beat frequencysignal will vary. with thepositior'i of the receiver. It should be noted that the e'ffect of frequency'drift in either transmitter is cancelled out, whereby ordinary equipment may be utilized without-anyloss of accuracy. a 7

By measuring the' phase' difference between beat frequencyisignals detectedby two spacedapart receivers, ajhyperbolic' line of positionfof the mobile transmitterrelative to the twdreceivers may be determined. Further, the greater the spacingjloetween' the receivers, the greater will be theaccuracy with which the line'of position may be determined. I l

T 'accomplish t is "nd, beat frequencysignals detected by a pair of fixedgspacedreceivers may be relayed to a common, point and, there amplified, and, fed toga cenvention'al phase meter adapted to indicate the phase diiference therebetween. ;The reference transmitter being'stationary, the phase'difference so determined will vary with differenceindistance between the mobile transmitter on, the onelhand andeach ofthe receivers on the other. So long as the difference injdistance between the mobile transmltter'and the tw receivers remains the same, .thejphase difierence between the'detected signals will not vary; Accordingly, it follows that if the mobile transmitter moves along ajhyperbolic path having the receivers, asfocal po ints,. no changein phase 1 differencewill be effected, while if the transmitter moves laterally; relative to such a path, a corresponding change in phase difierence will takeplace. j u

Accordingly, the phase difierence indicated by the phase meterwill be indicative of the p'osition of the mobile transmitterwith respect to a family of hyperbolas having the receivers '1 as focal points.) Using conventional transmission 'frej quencies and a distance between receivers consonant with great accuracy, the distance between receivers will be great relative to the wave length of transmission, and the ,familyQof hyperbolas will constitute a plurality or sectorsor lanes each defined by hyperbolic lines spaced one-half wave ence as indicated by a phase meter.

length apart where they intersect a straight base line drawn between'the receivers. Traverse of a lane so defined by the mobile transmitter will change the differential distance between the transmitter and the receivers one wave length, thereby effecting a 360 change in phase differ- It follows that ifthe zero. position of the phase meteris adjusted to correspond to position of the mobile transmitter on one ofthe lane-defining lines, the

Employing next receivers l4 and It and determining the phase difference between the signals detected thereby, aline of position of the mobile transmitter may be determined with much greater accuracy. In the example shown, receivers I4 and 16 are spaced apart .three wave lengths, whereby six lanes of position are establ ishedtherebetween, the;lanesbeing sepjarated by phase meter reading will directly indicate a line-= of position within a lane, although iii-Will not.

identify the lane wherein the transmitter lies. If two receivers are located at positions: spaced apart a distance not exceeding one-halfthe moso esta-blished is insuflici-ently accurate toindicate position with precision, but ityis an outstanding feature of the present invention to employ two receivers sospaced to determinerough position of the mobile: transmitter and obviate thereby the problem of lane identification.

In Fi ural is shown an: exemplary embodiment imaginary hyperbolic lines 23, having'receivers I4 and l 6 as focal points and separated one-half wave length where they intersect the baseline Accordingly, 'movement of the mobile transmitter from one line 23 tothe; nextv on either side will effect a 1 change of 360"i'n the phase diiference between extending. between the receivers.

' thebeat frequencies detected by receivers l4 and ,l 6-,-and.will effect a. corresponding complete revo lines of; position-.. intenmediate the lines of of the: system ofthe present invention, including a group of receivers 16, [5,1 6 and l i, receivers M and l5 being spaced apart a distance not exceeding one-half, the mobile transmitter wave length, and receivers Hi and 11 being spaced from receiver l4- atprogressively-greater distances... In conjunction with the-first group of; receivers is employed. a differently positioned group of re- .ceivers: l8, l9 and 20, preferably disposed on base lines-angulated relative to'thebase lines of the first group. Oi the second group,- receivers 18 and l flare' spaceda distance notexceeding half the wave length of transmission, and receivers l8 and '20 a greater distance. Receivers l8 and. may be employed as a; pairof thisgroup spaced an even greater distanceapart'.

Referring to .Figure 2,. assuming a position of mobile transmitter Ill as indicated, it will be readily understood that" the lines Of position of the mobil'etrans'mitt'er maybe readily established with respect to receiverpair1[4 l5 and receiver pair l8-l'9. ,That' is, the phase difference between the beat frequencies detected by receivers l4 1 51 will be indicative of jjthe' position of transmitter]! withfrespect to a family of hyperbolic line's illustratedlin' the drawing as dotted lines 2|, these lines having receivers II and. 15 as focal points. Similarly, the phase difference between the beat frequencies detected by receivers l8, and I9. will indicate the position of transmitter ll relative to a similar familyof hyperbolic lines illustrated as dotted lines 22. The receivers all being fix'ed'in position, the families of hyper.- bolic lines may be previously established and identified with phase meter readings, and employed as an overlay'with a map of the area, whereby the phase meter readings may be easily converted intolinesof position. In this manner, the phase meter readingsindicating difference in phase between the beat "frequency signals detected by receiver pairs l4| 5 and] 8-! 9 maybe utilized" to identify two rough lines of positions, whose intersection represents. the rough. position of the mobile transmitter.

lution of the phase meter. If the phase meter be zeroedtocorrespond to the lines of lane demarkation, the meter will indicate directly hyperbolic lane demarkation, with .-,great accuracy.

As. in.the:previous'case, a plot may beprevious- 1y established indicating the lines of lane. de-

. markation relative to the receivers, anda plurality of. intermediate-lines: of 'posi'tionin each lane. Employing'this plotas an overlay, the roughposition; of. the transmitter as established by receiver pairs I l-l5 and l 8--l9 w:i1l.immedi- :atelyidentify thelanein which thetransmitter is positioned, {the lane being thus identified, the phase differencebetween the signals detected by receivers and I6. may be utilized with the plot to establish the line of position of the transmitter withgreat accuracy.-.,Simi1arly,.,employing receiversl Qand 2G another; line of position oftranse mitter Il may be determined with-corresponding accuracy, the problemof lane identification-being again obviated by the rough position of thetransmitter previously determined. -The intersection of the linesof position. indicated by the receiver pairs [4-46 -andl8. 20',, then, will establish the fine position of the mobile transmitter, with. great accuracy. p r I U If even greater accuracy isreciuired, of the order sayof a few, feet. or inches, two receiver pairs "each sp'a'qzed.{apartmuch greater distances may be similarly employed In the embodiment shown, for examplejreceivers l4 and it maybe employed as one Widely spaced pair, and receivers t8 and i1 asftlie otherf'Again' using afproper plot indicating. thelines of lane demarkation betwe'een these receiver pairs and intermediate lines or position ineachlane, the lane of position of the transmitterrelative to the receiver pairs'is indicated by the transmitter position .al-. ready determined, andthe. phasedifferences between the'signal'sfdetected by the receiver pairs may be translated-iiito lines of position establishing the position of the transmitterwvith exceedingly great accuracy within a margin' pf error of'theloi der tra t" inches, if desired. ObViOliS-r ly, the greater distance between receivers of the receiver pairs employed in the final step, the

'more exact will bathe final position determine..-

Since ithe receivers are employed in pairsit willbe'apparent that the. receivers of each group need notbe arranged in line, nor need the groups be disposed .at a rightv angle or any other angle relative'to' each-other,- it being necessary only that the two pairs being used together to establisha positionbejdifferently located relative to each other. 1

The'position determination outlined above may be made within a very short time, a matter of a few seconds orlesS. In the system of Figure 2, for'eXample,-the signals detected by receivers I4, [5, l6, [8, I9 and may be relayed to'a common station located adjacent one of the receivers or at any other convenient point, as by telephone lines 24, cables, or radio links, to amplifiers 25, 26, 21, 28, 29 and 30 respectively. It is often desirable that these amplifiers be matched'and of a constant output type; The output of amplifiers and 26 may be supplied to a conventional phase meter 3|, Whose reading will indicate a rough line of position of the mobile transmitter relative to the receiver pair l4--l5. Similarly, the output of amplifiers 28 and 29 may be supplied to phase meter 32, Whose reading will indicate another rough line of position of the mobile transmitter relative to the receiver pair |8-.-|9. The output of amplifiers 25 and 21 may be supplied to a phase meter 33, and the output of amplifiers 28 and 30 to a phase meter 34. In this manner, on a proper .plot of the area previously established relative to the fixed position of the receivers, phase meters 29 and30 will indicate rough lines of position, establishing the rough position of the mobile transmitter. The rough position so determined immediately establishes thelane position of the transmitter relative to the receiver pairs l4 |6 and iii-20, and the phase meters 33 and 34 will indicate lines of position in those lanes by which the position of the transmitter may be established with greater accuracy. As previously indicated, if accuracy of the highest order is required, the receiver pairs l4|1 and l8l'l may be employed, utilizing another pair of amplifiers and another pair of phase meters, and a plot indicating the narrower lanes of position corresponding to the greater spacing between receivers of the receiver pairs. Obviously, the position information so determined may be radioed to the moving object by voice or code, if desired.

As indicated above, the signals detected by the various receivers may be transmitted to a common point by AM or FM radio links, if desired. Such an expedient is employed in the alternative embodiment illustrated in Figure 3, 'wherein the position determining phase meters are associated with the mobile transmitter. In this modification, the signal detected by each of the receivers is fed to an associated transmitter, similarly numbered and primed, by which each beat frequency signal detected may be transmitted to a receiver at the position of the mobile transmitter, the latter receivers being correspondingly numbered and double primed. The signals so detected, transmitted and received may be fed through the amplifiers in the manner previously described to the phase meters 3|, 32, 33 and 34, and the rough and fine position of the mobile transmitter derived therefrom in identical manner.

The foregoing relates to a two-dimensional navigation system and method. It will be apparent that if the transmission frequencies employed are such as to render it feasible, the system may be extended to three dimensions by arranging receiver pairs vertically or angularly relative to the ground. By employing a tunable reference transmitter, emissions from an unidentified object may be heterodyned, and the position of the object determined with great speed and ac curacy.

It will thus be seen that there has been provided by this invention a structure in which the various objects hereinbefore set forth, together with many practical advantages; are successfully achieved. As various possible embodiments may be made of the mechanical features of. theabove invention, all without departing. from thescope thereof, it "isto be understood that .all matter hereinbefore set forth or shown in the'accompanying drawings is to be interpreted as illustrative, and not in a limiting sense.

I claim: 1 w

1. Apparatus of the class described comprising two spaced transmitters adapted to transmit at different frequencies, a plurality of receivers adapted to detect the beat frequency between the emissions of said transmitters, one pair of said receivers being spaced apart a distance not exceeding half the Wave length of said emissions, another pair or said receivers being spaced apart a greater distance, and means for indicating the difference in phase between the beat frequencies detected by said receiver'pairs.

2. Apparatus of the class described comprising a mobile transmitter and a fixed transmitter adapted to transmit at frequencies difieririgby an audio note, a plurality of fixed receivers adapted to detect the beat frequency betweenthe emissions of said transmitters, one pairof said receivers being spaced apart a distance not exceeding half the 'wave length of said mobile transmitter, another pair of said receivers being spaced apart a greater distance, and means for indicating thedifference in phase between the beatfrequencies detected by each'o'f said receiverpairs.

3. Apparatus of the class described comprising a mobile transmitter and a fixed transmitter, said transmitters being adapted to transmit at frequencies differing by an audio note, three fixed receivers each adapted to detect the beat frequency between the emissions of said transmitters, the second of said receivers being spaced from the first receiver a distance not exceeding half the wave length of said mobile transmitter and the third receiver being spaced from the first receiver a greater distance, means for indicating the diiference in phase between the beat frequencies detected by said first and second receivers, and means for indicating the difference in phase between the beat frequencies detected by said first and third receivers.

4. Apparatus according to claim 3, wherein said phase difference indicating means are located in the vicinity of one of said receivers.

5. Apparatus according to claim 3, wherein said phase difference indicating means are mobile with said mobile transmitter.

6. Apparatus of the class described comprising a mobile transmitter and a fixed transmitter adapted to transmit at diiferent frequencies, a plurality of fixed receivers each adapted to detect the beat frequency between the emissions of said transmitters, one pair of said receivers being spaced apart a distance not exceeding half the wave length of said mobile transmitter, other pairs of said receivers being spaced apart greater but different distances, and means for indicating the difference in phase between the beat frequencies detected by each of said receiver pairs.

7. Apparatus of the class described. comprising I phase between the beat frequencies detected by each of said receiver-pairs. e

v 8. Apparatus of the class described comprisin a mobile transmitter and a fixed transmitter adapted to transmit'at different frequencies, a firstgroup of receivers each adapted to detect the beat frequency between the emissions of said transmitters, a second group of receivers each adapted to detect the beat frequency between the emissions of said transmitters, said groups being differently positioned relative to said transmitters, one pair of receivers of each group being spacedapart a distance not exceeding half the wave length of said mobile transmitter, another pair of receivers of each group being spaced.- apart a greater distance, and means for indicating the difierence in phase between each of said receiver pairs. v

9., Apparatus of the class described comprising a mobile transmitter and a fixed transmitter, said transmitters being adapted, to transmit at frequencies differing by an audio note, a first group of fixed receivers each adapted to detect the beat frequency between the emissions of said transmittersp a second group of fixed receivers each adapted to detect thebeat frequency between the emissions of said transmitters, said groups being angularly positioned relative to said .mobile transmitter; one pair of receivers of each group 8 7 being spaced. apart a distance notexceeding half thewave length of saidmobiletransmitter, another pair of receivers of each group .beingspaced apart a greater distance, and means for indicating the difierence in phase between each of said receiver pairs.

10. Apparatus of the class described comprising two spaced transmitters tuned to transmit different frequencies, a plurality of receivers adapted to detect the beat frequency between the emissions of said transmitters, one pair of .receivers being spaced apart a first distance and another pair of receivers being spaced apart a greater distance, means for indicating a difference in phase between the beat frequency detected by each of said receiver pairs, the said first distance being sufiiciently limited so. that the phase relationship of the beat frequencies as detected' by said first pair of receivers provides a position without ambiguity over a known'range of movement of one of said transmitters; whereby the indicated phase relationship of the beat frequencies as detected by the'second pair of receivers may be construed without'ambiguity.

' CHARLES E. HASTINGS.

REFERENCES CITED The following references are of recordin the file of this patent:

UNITED STATES PATENTS Hawkins a. July 4, 1950 

